1. Field of the Invention
The present invention relates to novel silica-based granular particulates, to various processes for the preparation thereof, and to the use of such novel silica particulates as reinforcing fillers for elastomeric matrices.
2. Description of the Prior Art
It has long been known to this art to use precipitated silica as a white reinforcing filler material for elastomers.
However, like any reinforcing filler, it must be suitable for processing and easily formulated into mixtures.
Its powder form is unsatisfactory to the extent that it gives rise to an appreciable amount of dust and is slow to be formulated into mixtures (low apparent density).
A granular form has heretofore been proposed which provides an appropriate solution for the aforesaid two problems, but which often results in inadequate dispersion of the filler in elastomeric matrices.
Various solutions too have been proposed to avoid this particular disadvantage.
Thus, European Patent No. 18,866, assigned to the assignee hereof, describes granular silica materials in the form of homogeneous spheres having a mean particle size greater than 80 .mu.m, in particular from 200 to 300 .mu.m.
The spherical particulates are made by atomizing a precipitated silica suspension.
Because of its properties, this type of product was found to be especially attractive for reinforcing elastomers.
However, need still exists for an improved product in respect of one or possibly several aspects at the same time. Thus, the need remains in this art for silica particulates having a potentially higher and more homogeneous granulometry, which are denser, have an even lower proportion of fines, and which are less fragile.
Moreover, the preparative processes for granules and especially those described above, conventionally entail the use of atomizers. These devices impose certain requirements on the suspensions to be atomized, especially with regard to the dry solids content thereof, which cannot exceed a certain maximum value. They also entail considerable maintenance.
These processes also suffer from the disadvantage of limiting the products obtained to a certain granulometry range, especially because of the low dry solids content mentioned above.
Thus, another problem exists in this art, namely, simplifying the processes for the preparation of silica particulates and enhancing the number of options provided thereby.